The present invention relates to an electric motor, in particular for hand powered tools.
In a known electric motor of this type, a central shaft opening is punched in a metal plate pack of the rotor or the stator, and the metal plate pack with the end plates of insulating material is fitted on the rotor shaft so that, at both sides of the plate pack the rotor shaft extends axially outwardly with a corresponding shaft portion. Bearing seats for receiving a rotary bearing are formed on the shaft portions, and a pinion for the torque transmission is fixed on one shaft portion. The connection between metal plate pack and the rotor shaft is produced by a plastic injection molding process. Simultaneously a plastic longitudinal insulation between the rotor shaft and the metal plate pack is produced. In the event of failure, it must prevent a voltage propagation from the rotor winding to the outwardly located, contacting components. The synthetic plastic longitudinal insulation must have a certain thickness because of the corresponding regulations and safety reasons, and must maintain the required testing voltage. For avoiding a voltage propagation by strong dirtying in the bearing region, and also in the event of failure of a commutator, through the armature shaft and the bearing outwardly, a labyrinth disk is applied on the longitudinal insulation for creep resistance and distance increase. The grooves in the plate pack for receiving the rotor winding are coated with press board and are closed and impregnated after the winding with the pressed board.
Accordingly, it is an object of the present invention to provide an electric motor, in particular for hand powered tools which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in an electric motor in which the groove coatings and the end plates as well as the rotor shaft with the shaft are injection molded in an injection molding process from synthetic plastic.
When the electric motor is designed in accordance with the present invention, it has the advantage that on the one hand the production of the motor is substantially simplified, and on the other hand, a voltage propagation outwardly in the event of failure is reliably prevented without additional measures. Since the shaft opening is absent and the longitudinal insulation is absent, the magnetic flux in the iron cross-section is hindered substantially less and the remagnetization losses which are produced in a conventional electrical machines by high backload and frequency in back iron are substantially reduced. The idling speed of the rotor is lowered and thereby the winding design in the loading point can be improved. With the new cross-sectional design of the metal plates, the field diameter of the rotor with the same power can be reduced. By complete synthetic plastic coating of the metal plate pack, the danger of a wire damage during winding process of the rotor winding is lowered. Since the rotor must withstand high temperatures during overloads, a high temperature resistant synthetic plastic or a duroplastic can be utilized.
In accordance with a preferable embodiment of the invention, a plurality of longitudinal throughgoing axial openings can be provided in the plates, for filling the synthetic plastic during the injection molding process. Preferably, the openings are arranged on web feet between the grooves and alternate with the depression for the punch acting, so that in the peripheral region of the metal plate pack, each depressions follows an opening and vice versa.
In accordance with a preferable embodiment of the present invention, the rotor winding which is inserted in the grooves of the metal plate pack surrounds its winding heads which project over the end side of the metal plate pack, the end plates and the shaft end and is coated in a dipping or impregnating process. With this structural design, a very high stability of the rotor is obtained which is required for high rotary speeds. The winding heads additionally contribute to the stabilitation of the armature plate pack and the dipping or impregnation of the rotor winding makes possible glueing and backing of the winding heads, and plates end shaft ends, which together advantageously influences the strength of the rotor.
In accordance with a preferable embodiment of the invention, a bearing pin for example of steel is injection molded in at least one shaft end, as an insert aligned with the shaft end. A rotary bearing, in particular a ball bearing and/or a collector is non rotatably received on the pin part which freely projects from the shaft end. The rotary bearing and the collector are preferably pressed on the bearing pin. A danger of the breakthrough of the voltage to the bearing pin and thereby a voltage propagation to the outwardly located components which are accessible for contacting by a user, does not take place in this case.
In accordance with a preferable embodiment of the present invention, at least one bearing pin extends up to the metal plate pack and is firmly connected at an end side with an anchoring disk which is enclosed in the end plate. For weight reduction, hollow bearing pins and anchoring disks can be formed as one piece deep drawn parts. The anchoring disk is provided on its disk periphery with a circumferential set of teeth, in order to improve adherence in synthetic plastic and thereby to provide greater safety against relative movement of the bearing pin and the metal plates.
In accordance with a preferable embodiment of the present invention a pin part of the bearing pin which projects in the end portion outwardly beyond the shaft end has an outer or inner thread for outer or inner screwing of a drive pinion or a drive gear. Alternatively a pinion end is injection molded in the shaft end as an insert which is in alignment with the shaft end. The pinion end with its pinion teeth freely projects outwardly from the shaft end. Bearing pins or pinion ends are inserted during the injection molding process in the mold and injected from synthetic plastic of the shaft end.
In accordance with a preferable embodiment of the invention, the grooves which are formed in the synthetic plastic layer are provided with a groove closure. The groove closures are injection molded in the injection molding process as a film hinge on the groove coating. During the injection molding process the region of the groove lock serves in synthetic plastic filling process for producing the groove coating. The groove locks produced at the end of the filling process are folded after insertion of the rotor winding over the groove openings. Tooth strips which are formed in an opposite groove flank and produced also during the injection molding process, are arrested in a zipper-like manner and secure the rotor winding in the grooves.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.